The electrophoretic effect is well known and the prior art is replete with a number of patents and articles which use and describe the effect. See for example, U.S. Pat. No. 5,077,157 issued on Dec. 31, 1991 and entitled Methods of Fabricating Dual Anode Flat Panel Electrophoretic Displays. See U.S. Pat. No. 4,850,919 entitled Monolithic Flat Panel Display Apparatus and Methods for Fabrication Thereof issued on Jul. 25, 1989, see U.S. Pat. No. 5,505,763 entitled Dual Anode Flat Panel Electrophoretic Display Apparatus, issued on Oct. 1, 1991. The above patents are all assigned to CopyTele, Inc., the assignee herein with Frank J. DiSanto and Denis A. Krusos, the named inventor and the inventors herein. As will be recognized by a person skilled in the art, the electrophoretic effect operates on the principle that pigment particles, when suspended in a medium, can be electrically charged and thereby caused to migrate through the medium to an electrode of opposite charge. Electrophoretic image displays (EPID) utilize the electrophoretic effect to produce desired images. In a EPID, colored dielectric particles are suspended in a fluid medium of an optically contrasting color. The colored electrophoretic particles are then caused to selectively migrate against a transparent screen, thereby displacing the fluid medium against the screen and creating the desired image.
In a conventional EPID, a volume of an electrophoretic dispersion is encapsulated in between an anode structure and a cathode structure. Conventionally to create an image in an EPID, the dielectric pigment particles in the dispersion are caused to migrate toward the cathode structure. The cathode structure is transparent, consequently as the pigment particles displace the suspension fluid against the cathode structure, the desired image can be formed. The response time of an EPID is dependent upon the time it takes the pigment particles to migrate through the suspension medium and reach the cathode structure. Consequently, in an attempt to create more efficient EPIDs, EPIDs have been formed having very small interstices in between the anode structure and the cathode structure. Such constructions therefore lessen the distance the pigment particles must migrate and consequently effect the response time capabilities of the EPIDs.
A problem with EPIDs having small spacings between their anode and cathode structures, is how to fill the EPIDs with the needed pigment particles and suspension fluid. In EPIDs having a spacing of 0.007 inches or more between its anode and cathode structures, the EPID is filled by introducing a dispersion of pigment particles and suspension fluid into the EPID chamber with a pipette filler or similar device. However, with EPIDs having a fluid chamber with a spacing of less than 0.007 inches, pipette filling techniques are not as effective. With spacings of less than 0.007 inches, the suspension fluid readily enters the fluid chamber. However, due to their size and bulk, the pigment particles accumulate near or at the entrance of the chamber. For EPIDs having spacing of less than 0.003 inches, the pigment particles become trapped at the point of insertion and fail to flow altogether. Consequently, the design of narrow chambered EPIDs is become limited by a manufacturers ability to fill EPIDs with dispersions, thereby hindering advancements in EPID technologies available through EPIDs having an interstice spacing of less than 0.007 inches.
It is, therefore, a primary objective of the present invention to provide a method of filling EPIDs having an interstice spacing of less than 0.007 inches with a proper dispersion of pigment particles and suspension fluid.